1. Field of the Invention
The present invention relates to a method of making 4-hydroxy-4'-benzyloxydiphenyl sulfone.
2. Related Background Art
It has been known that 4,4'-dihydroxydiphenyl sulfone -monobenzyl ether can be made when 4,4'-dihydroxydiphenyl sulfone(hereinafter abbreviated as BPS) and a benzyl halide (X--CH.sub.2 C.sub.6 H.sub.5, where X indicates a halogen element) are reacted as materials in the presence of an alkali catalyst. As for its reaction solvent, both organic solvent system and aqueous solvent system have been known as well.
One of problems in such a method of making BPS-monobenzyl ether, in its industrial method in particular, is a problem of reaction selectivity in that 4,4'-dibenzyloxydiphenyl sulfone (hereinafter abbreviated as BPS-dibenzyl ether) is generated as a byproduct since BPS, which is a reaction material, has two phenolic hydroxyl groups. Such a problem of reaction selectivity results in difficulty in controlling reaction conditions, necessity for a step of isolating the product, and so forth. Another problem lies in the amount of solvent required for the reaction; it is preferably as small as possible from the viewpoint of the manufacturing apparatus, easiness in manufacturing condition control, manufacturing cost, and the like.
Japanese Patent Application Laid-Open No. 58-82788 discloses a manufacturing method in an organic solvent (dimethyl formamide) using BPS and benzyl chloride, in which an alkali metal carbonate is employed as a catalyst. This reaction is insufficient in terms of reaction selectivity, thus further necessitating a purification process by use of extraction or recrystallization. Japanese Patent Application Laid-Open No. 59-225157 and No. 4-210955 disclose a method of making BPS-monobenzyl ether comprising the steps of dissolving BPS by an alkali compound using water as a reaction solvent, further reacting benzyl chloride therewith, and isolating the resulting product. Japanese Patent Application Laid-Open No. 5-117224 discloses a manufacturing method in which, upon a reaction under a similar condition, an alkali compound is added to the aqueous reaction solution such that the latter attains a pH of 7.5 to 8.5. In such an aqueous solvent reaction system, a large amount of unreacted BPS would exist in the product mixture in order to restrain BPS-dibenzyl ether from occurring, thus necessitating a complicated purification process such as solvent extraction or recrystallization. Further, water as the solvent is necessary in an amount about 10 times that of BPS, thus making it problematic not only in that production per unit volume of the manufacturing apparatus is small but also in processing of such a large amount of waste solvent.
Accordingly, in a method of making BPS-monobenzyl ether, there has been a strong demand for a method having a high reaction selectivity, making a highly pure product without requiring a complicated purification process such as extraction or recrystallization, yielding a high quantity of production per unit volume of reaction solvent, and capable of minimizing the reaction waste liquid.